Anisotropic Colossal Magnetoresistance Effects in Fe_{1-x}Cu_xCr_2S_4

摘要

A detailed study of the electronic transport and magnetic properties ofFe$_{1-x}$Cu$_x$Cr$_2$S$_4$ ($x \leq 0.5$) on single crystals is presented. Theresistivity is investigated for $2 \leq T \leq 300$ K in magnetic fields up to14 Tesla and under hydrostatic pressure up to 16 kbar. In additionmagnetization and ferromagnetic resonance (FMR) measurements were performed.FMR and magnetization data reveal a pronounced magnetic anisotropy, whichdevelops below the Curie temperature, $T_{\mathrm{C}}$, and increases stronglytowards lower temperatures. Increasing the Cu concentration reduces thiseffect. At temperatures below 35 K the magnetoresistance, $MR = \frac{\rho(0) -\rho(H)}{\rho(0)}$, exhibits a strong dependence on the direction of themagnetic field, probably due to an enhanced anisotropy. Applying the fieldalong the hard axis leads to a change of sign and a strong increase of theabsolute value of the magnetoresistance. On the other hand themagnetoresistance remains positive down to lower temperatures, exhibiting asmeared out maximum with the magnetic field applied along the easy axis. Theresults are discussed in the ionic picture using a triple-exchange model forelectron hopping as well as a half-metal utilizing a band picture.